June 22, 2011 -- Avoiding weight gain as you age isn't impossible, after all.

If you yearn to be among those who sail through the years without picking up a pound for each birthday, Harvard doctors have a game plan for you. And it goes far beyond the old "eat less, exercise more" mantra.

Reducing your intake of specific foods, sleeping 6 to 8 hours nightly, getting some exercise, and turning off the TV all predicted less weight gain with time, they found.

They also found five foods strongly linked with weight gain and five others linked with less than average weight gain.

''The message here is that the type and quality of food and beverage one eats are incredibly important," says researcher Dariush Mozaffarian, MD, DrPH, associate professor of medicine and epidemiology at Harvard School of Public Health, Brigham and Women's Hospital and Harvard Medical School.

The new research, he says, ''shows how multiple lifestyle factors, including diet, were related to long-term weight gain."

The study appears in the New England Journal of Medicine.

Avoiding Weight Gain: Study Details

The researchers wanted to focus on what leads to long-term weight gain and why the average adult gains about a pound a year.

They tracked 120,000 participants in three studies, the Nurses' Health Study, the Nurses' Health Study II, and the Health Professionals Follow-up Study. Every four years, they evaluated the links between changes in lifestyle habits and weight.

On average, the study participants gained an average of 3.35 pounds over each four-year period. That added up to nearly 17 pounds after 20 years. At the start of the three studies, the men and women's average ages were 37, 50, and 52.

5 Foods That Make You Fat; 5 That Don't

When the researchers looked more closely, they found five foods associated with the greatest weight gain over the study period:

Potato chips

Other potatoes

Sugar-sweetened beverages

Unprocessed red meats

Processed meats

They also found five foods linked with less gain and even weight loss:

Vegetables

Whole grains

Fruits

Nuts

Yogurt

Deciphering the Findings

"There were huge differences in four-year weight gains based on what people did," he says. "The quantity of fat in the food didn't seem to be strongly related to weight gain." For instance, no differences were seen for low-fat or skim milk compared to whole-fat milk.

Rather, he says, focusing on the quality of food -- not simply total calories, or fat grams, or grams of carbohydrates -- seems most important in avoiding weight gain.

They write: "A habitual energy imbalance of about 50 to 100 kilocalories per day may be sufficient to cause the gradual weight gain seen in most persons."

Yogurt was perhaps the biggest surprise on the list of foods linked with less weight gain, Mozaffarian says. The researchers aren't sure why. They cite some other research finding that changes in gut bacteria from eating yogurt may help in weight control. Or those who eat yogurt may have other healthy habits.

Changes in diet had the strongest link to weight gain. However, the researchers also found that those who slept 6 to 8 hours a night gained less than those who slept less than 6 or more than 8. Weight gain was also linked with changes in the amount of television viewing and changes in physical activity.

''Small differences add up over time," Mozaffarian says. He sees that as both ''a danger and an opportunity." If you don't pay attention, he says, the pounds can pile on quickly. "If you do pay attention, a handful of changes could add up in a beneficial way," he says.

He is not suggesting people completely avoid foods linked with weight gain. "If someone wants to eat some of the foods on the list associated with weight gain, as long as they eat a lot of other foods that are not associated with weight gain, and exercise, and not watch a lot of TV, that would be OK," he says.

Mozaffarian reports receiving honoraria from Unilever, Aramark, and other food-related companies for speaking on diet-related topics.

Avoiding Weight Gain With Age: Perspective

The study provides some good support for factors other experts have assumed are linked with weight gain, says Connie Diekman, RD, director of university nutrition at Washington University in St. Louis. She reviewed the study but was not involved in it.

Diekman says that among the most interesting findings is that the lower the intake of fruits, vegetables, whole grains, nuts, and yogurt, the more significant the weight gain. That result jibes with the recommendation in the Dietary Guidelines to shift food intake to more plant foods.

Another important finding, she tells WebMD, is that "a shift in calorie intake of as little as 50 to 100 calories a day may be all it takes to gain or lose weight."

Advice? "I'd encourage consumers to think about one portion you can cut down on each day or one 10-minute walk you can add to your day. These small steps can then become the steps on the path you need to make more changes to achieve, and maintain, a healthier weight."